Effects of atmosphere composition on fabrication process of hollow glass microspheres in drop-tower furnace

To fabricate high quality hollow glass microspheres (HGMs) for inertial confinement fusion (ICF) targets by solgel technology, effects of furnace atmosphere composition on the transformation process from gel particles to HGMs and the resulting quality of HGMs were investigated by numerical simulation and experiments. The results show that the furnace atmosphere composition significantly affects the heat and mass transfer process between particles/microspheres and furnace atmosphere, but the falling velocity of the particles/microspheres in drop-tower furnace changes only slightly with the furnace atmosphere compositions. The heating-up rate of gel particles in heat-absorbing stage increases remarkably with the increase of the content of helium in the furnace atmosphere and increasing the helium content accelerates effectively the encapsulation of gel particles. Consequently, higher helium content in furnace atmosphere will result in higher HGM yield with high quality and larger HGM aspect ratio. However, maintaining a proper proportion of helium in the furnace atmosphere is necessary to improve HGM surface smoothness. With the volume percentage of helium ranging from 50% to 80%, HGMs with high sphericity, concentricity and surface smoothness can be fabricated with high yield. (authors)